A silicon single crystal by the Czochralski method is manufactured using a vitreous silica crucible. The silicon single crystal is manufactured by melting high-purity polysilicon to obtain a silicon melt, pulling up while rotating a seed crystal with the tip of the seed crystal contacted with the surface of the silicon melt. In order to maintain a solid-liquid interface of the silicon melt central part, which is contacted with the single crystal, to be near the silicon melting point of 1420° C., the temperature of the vitreous silica crucible is as high as about 1450-1600° C. In pulling of silicon single crystal which can last 2 weeks, the extent of deformation of a sidewall sagging at a rim portion of the vitreous silica crucible may be 5 cm or more.
The size of the vitreous silica crucible is, 28 inches (about 71 cm), 32 inches (about 81 cm), 36 inches (about 91 cm), and 40 inches (about 101 cm) etc., in diameter. A crucible with a diameter of 101 cm is an enormous crucible having a weight of about 120 kg, and the mass of silicon melt contained therein is 900 kg or more. That is, during the pulling of silicon single crystal, 900 kg or more silicon melt of about 1500° C. is contained in the crucible.
Such vitreous silica crucible is suitable for manufacturing a large-size single-crystal silicon ingot with a diameter of 200 to 450 mm (for example: 200 mm, 300 mm, 450 mm) and a length from 1 m to 5 m or more. A single-crystal silicon wafer manufactured from such large-size ingot is suitable for manufacture of flash memory or DRAM.
A silicon wafer used for manufacture of semiconductors is obtained by slicing a silicon single crystal. With the high integration of semiconductor devices in recent years, the reduction of void defects in the surface of a silicon wafer is in demand.
It is known that void defects can be removed by etching the wafer surface layer, but the production of a silicon single crystal without void defects is desired from the electronics field because the etching process is time-consuming and costly.
Various methods are known to produce a silicon single crystal without void defects. One is a method of reducing the bubbles in the transparent layer of a vitreous silica crucible for pulling of the silicon single crystal. The vitreous silica crucible for pulling of the silicon single crystal is manufactured using a silica powder. According to the rotating mold method, the vitreous silica crucible is manufactured by processes of (1) depositing silica powder in a rotating mold, and (2) melting the silica powder by arc discharge. The mixing of bubbles in the silicon single crystal is considered to be one cause of void defects. Therefore, in order to avoid bubbles mixing into the silicon single crystal, a transparent layer of the vitreous silica crucible is formed from a layer without bubbles.
In order to manufacture a vitreous silica crucible having a transparent layer, that is, a substantially bubble-free layer, a manufacture method of vitreous silica crucible using a rotating mold capable of sucking out the gas component inside the mold is known. Specifically, it is a method of depositing a silica powder on the inner face of the mold and then arc melting while exhausting the gas component by a suction apparatus (Patent Literature 1). Furthermore, Patent Literature 2 discloses a method of determining whether or not a cause of bubbles in the vitreous silica material exists.